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XRT79L71
PRELIMINARY
535
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
The Trail-Trace Message consists of a 16-byte string that is repeatedly transmitted from one terminal to the
remote terminal equipment. The byte-format of the Trail-Trace Message is presented below in Table 66.
The very first byte of this 16-byte string is referred to as the Frame Start Marker byte. The Frame Start Marker
byte is typically of the form [1, C6, C5, C4, C3, C2, C1, C0]. This "1" in the MSB (most significant bit) of this
first byte is used by a Receiving Terminal to identify this byte as the Frame Start Marker byte.
All of the
remaining bytes within a given Trail-Trace message will contain a "0" in their MSB. The bits C6 through C0
typically contains the results of a CRC-7 calculation that was performed over the previous 16-byte Trail-Trace
Message frame.
NOTE: The XRT79L71 will NOT compute nor verify this CRC-7 value that is residing within these bit-fields. The user will
need to externally compute and verify the CRC-7 value over a given inbound Trail-Trace Message.
The remaining 15 bytes are used for the transport of 15 ASCII characters which transport the actual Trail-Trace
message. Typically, these Trail-Trace Messages are used to transport messages that are of content/protocol
that are compliant to some of the requirements as listed in ITU-T G.831 and E.164.
NOTE: As mentioned earlier, the MSBs (most significant bits) within the each of the 15 remaining (e.g., non-Frame Start
Marker byte) MUST be set to "0".
6.3.3.2
CONFIGURING THE XRT79L71 TO RECEIVE TRAIL-TRACE MESSAGES
The XRT79L71 contains a total of 16 Receive Trail-Trace Message Registers, and 16 Transmit Trail-Trace
Message Registers.
The role of the Transmit Trail-Trace Message Registers is described in
As mentioned earlier, the XRT79L71 contains 16 Receive Trail-Trace Message Registers (e.g., Receive Trail-
Trace Message Register - Byte 1 through Receive Trail-Trace Message Register - Byte 16). The purpose of
these registers is to permit the user to read out and process the contents of the incoming Trail-Trace Message.
For Trail-Trace Message purposes, the Receive Trail-Trace Message Controller block along with the Receive
DS3/E3 Framer block will group 16 consecutive inbound E3 frames, into a Trail-Trace Message Super-Frame.
As the Receive Section of the XRT79L71 is receiving the very first E3 frame within this Trail-Trace Message
Super-Frame, it will read out the contents of the TR byte within this particular E3 frame, and it will write that
value into the Receive Trail-Trace Message Register - Byte 1. When the Receive Section of the XRT79L71 is
receiving the second E3 frame within this Trail-Trace Message Super-Frame, then it will read out the contents
of the TR byte within this second E3 frame and it will write that value into the Receive Trail-Trace Message
Register - Byte 2. As the Receive Section of the XRT79L71 is receiving each subsequent E3 frame, within this
particular Trail-Trace Message Super Frame, it will continue to read out the contents of the TR byte-fields
within these incoming E3 frames, and it will continue to increment to, and write the contents of these TR bytes
into the very next Receive Trail-Trace Message Register. After the Receive Section of the XRT79L71 has
received the 16th inbound E3 frame, within this Trail-Trace Message Super-Frame (e.g., it has read out the
contents of the TR byte-field within this 16th E3 frame, and has written the contents of this TR byte into the
Receive Trail-Trace Message Register - Byte 16), it will begin to receive and process the TR bytes within a new
incoming Trail-Trace Message Super-Frame. As the Receive Section of the XRT79L71 does this, it will repeat
TABLE 66: THE BYTE-FORMAT OF THE TRAIL-TRACE MESSAGE THAT THIS BEING TRANSPORTED VIA AN E3 DATA-
STREAM VIA THE TR BYTE
BYTE NUMBER
BIT 1
(MSB)
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
(LSB)
1 (FrameStart
Marker)
1
CRC_Value[6:0]
2
0
TTM_Byte_1[6:0]
*
0
TTM_Byte_N[6:0]
15
0
TTM_Byte_15[6:0]
16
0
TTM_Byte_16[6:0]